The field of this invention is fluid analyte concentration determination, particularly optical based protocols, e.g., reflectance or transmission measurement based analyte concentration determination.
Analyte measurement in physiological fluids, e.g., blood or blood derived products, is of ever increasing importance to today""s society. Analyte detection assays find use in a variety of applications, including clinical laboratory testing, home testing, etc., where the results of such testing play a prominent role in diagnosis and management in a variety of disease conditions. Analytes of interest include alcohol, formaldehyde, glucose, glutamic acid, glycerol, beta-hydroxybutyrate, L-lactate, leucine, malic acid, pyruvic acid, steroids, etc.
In response to this growing importance of analyte measurement, a variety of analyte measurement devices for enabling patients to test their own blood for the presence and concentration determination of a variety of different analytes are well known in the art. Of great interest and use in this area are optical based measurement devices in which a sample is illuminated and reflected light therefrom is detected to obtain an analyte concentration.
One such device is shown in U.S. Pat. No. 4,552,458, to Lowne, which deals with a compact reflectometer to enable the exposure of a reagent to different light beams, one red and one green. The light beams are folded by a reflecting surface, which redirects the beams through a transparent glass plate onto a reagent strip. Light is reflected back from the strip along a similar folded path onto a detector located in the same plane as the light sources.
Other patents describing various optical arrangements for illuminating and detecting the light reflected from reagent strips are U.S. Pat. No. 4,632,559, to Miles, for an optical read head for measuring non-specular, i.e., non-mirror-like, reflections from a reagent test strip; U.S. Pat. No. 4,787,398, to Garcia, for a glucose medical monitoring system and U.S. Pat. No. 4,985,205 for a test carrier analysis system. The latter ""205 patent describes a reference measurement using the same optical elements by using the same reference layer so as to avoid a two tier testing process. The reference measurement uses two LED""s for illuminating the same color formation layer from different directions. The LED""s are preferably activated successively so that the measurements can then be averaged.
U.S. Pat. No. 5,039,225 describes a device for measuring optical density with a light transmissive plate inserted between the light source and the surface being measured. The light is directed at an angle relative to a surface of the plate so that a portion is reflected back to a detector for obtaining a reference measurement while another detector is oriented to detect diffuse light for analysis.
A characteristic of methods and devices that provide for glucose determination using a measured reflectance value is that temperature can have an impact on the final measurement, as both the optical components and chemistry are temperature sensitive. For example, light output from light emitting diodes modulates in response to ambient temperature changes. Various attempts have been made to correct for this temperature effect in reflectance measurement instruments. For example, in U.S. Pat. No. 5,995,236 and WO 99/23479, control loops are employed which measure a change in temperature and modulate the current to the light emitting diode to therefore provide for a constant output from the diode. See also U.S. Pat. No. 5,843,692 where a similar approach is employed to compensate for the temperature sensitivity of the light emitting diode.
Despite the above assay devices and protocols that have been developed, there is a continued need for further innovation in the field of optical, e.g., reflectance, measurement devices for analyte concentration determination. Of particular interest would be the development of a device that is able to accurately provide a temperature corrected analyte concentration value without the use of additional temperature sensing components, e.g., thermistors, additional diodes or detectors above those required for reflectance measurement, etc. Of particular interest would be the development of a device and method in which the power supplied to the illumination means is not modulated to compensate for temperature sensitivity.
Relevant Literature
U.S. Patents of interest include: U.S. Pat. Nos. 3,686,517; 4,529,949; 4,552,458; 4,632,559; 4,787,398; 4,985,205; 5,039,225; 5,049,487; 5,059,394; 5,477,853; 5,843,692; 5,995,236; 5,968,760. Also of interest is WO 99/23479.
Optical based methods and devices are provided for determining the concentration of an analyte in a fluid sample. In practicing the subject methods, a fluid sample is applied to a matrix impregnated with a signal producing system. The signal producing system produces a detectable product in an amount proportional to the amount of analyte in the sample. A surface of the matrix is then illuminated and an optical, e.g., reflectance, measurement is obtained therefrom, generally following a predetermined incubation period. An optical component, preferably the illumination or light detection means, is also employed to obtain a temperature value corresponding to the ambient temperature of the matrix. The analyte concentration of the sample is then obtained from the optical measurement using an algorithm that employs the optical component derived temperature value. The subject methods and devices are suited for use in the detection of a variety of different types of fluid analytes, and are particularly suited for use in detecting the concentration of glucose in whole blood.